1. Field of the Invention
This invention relates to rigid and flexible plugs for use in wellbores and particularly to plugs for use in cementing operations and cementation preparation operations in cased wellbores.
2. Prior Art
Plugs are used for various purposes in wellbores and in wellbore operations In cementing operations, plugs with flexible wipers are used to act as a barrier between cement and displacement fluid to prevent fluid/cement intermingling; to wipe off fluid such as drilling mud or cement from the interior casing wall; to provide means for indicating when cement has been displaced from within the casing; and to permit passage of the plug through portions of the casing string which are impassable to rigid plugs.
The available plugs have proven to be unsatisfactory. The flexible wipers must be flexible enough to pass through restrictions in the casing string. Plugs that exhibit such flexibility are not rigid enough to provide adequate wiping action. Also the flexible wipers deteriorate, disintegrate, and crack under normal operating conditions. Damaged wipers cause a plug to be off center thereby preventing the accurate and effective seating of the plug end. Failure of the plug to seal results in unwanted intermingling of wellbore fluids and cements and can make it impossible to engage in secondary operations such as the operation of an inflatable packer or of a stage tool.